1. Field of the Invention
The present invention relates to a granular photocatalytic material that decomposes organic matter using light energy, a production method therefor, a functional restoration method therefor, and an apparatus for decomposing and removing toxic organic matter. More particularly, the present invention relates to a granular photocatalytic material that is superior in durability, water resistance and chemical resistance, a functional restoration method therefor, and an apparatus for decomposing and removing toxic organic matter.
2. Description of Related Art
A photocatalytic reaction is a reaction wherein organic matter is decomposed by using a photocatalyst in the presence of light energy. This reaction has widely been studied as a technology of decomposing toxic organic matter using ultraviolet light included in light emitted from the sun, or indoor lighting such as fluorescent lamps or incandescent lamps for the purpose of purification of water or air, and for building materials such as tiles.
Titanium dioxide particles or a thin titanium dioxide film, that is formed by firing an alkoxide solution of metallic titanium, has generally been used as the photocatalyst.
When using fine titanium dioxide particles, there may be mentioned a method of using fine titanium dioxide particles as they are, a method of fixing fine titanium dioxide particles on solid matter using a binder, or a method of mixing fine titanium dioxide particles with a paint or hydrate, applying the mixture on solid matter, and drying the mixture, thereby fixing the fine titanium dioxide particles on the solid matter. When using an alkoxide solution of metallic titanium, the thin titanium dioxide film is formed by a so-called sol-gel method of applying the solution on solid matter, followed by drying and firing.
There is also a method of forming a thin titanium dioxide film on solid matter by a CVD method or a sputtering method.
When using fine titanium dioxide particles as they are, there is a merit such that high photoactivity and high decomposability of the organic matter are achieved because the fine titanium dioxide particles have a large surface area and therefore exhibit high adsorptivity of the organic matter. However, the fine titanium dioxide particles are not easily handled because the average particle diameter is from about 5 to 300 nm, and it is hard to control the position when used in air or liquid. When the fine titanium dioxide particles are scattered or dispersed, the fine titanium dioxide particles cause scattering of ultraviolet light, have poor light efficiency, and are not easily recovered.
When the fine titanium dioxide particles are used in a state of being fixed on the solid matter using a binder, a problem arises in that the decomposition efficiency of the organic matter is lowered because of a small contact area between the fine titanium dioxide particles and the organic matter, oxygen, or ultraviolet light. When using an organic binder, a problem arises in that the binder itself is decomposed by the fine titanium dioxide particles.
When a thin film of titanium dioxide is formed from an alkoxide solution of metallic titanium on the solid matter using a sol-gel method, there is a merit such that the film can be formed in a small space without exerting any influence on the form of the solid matter and an anatase crystal can be produced by firing at a temperature of 600° C. or lower. However, a long time ranging from 5 to 6 hours is necessary, to produce the thin film by firing at this temperature, and the production conditions are difficult to control. Also, since the thin film has a smaller contact area with the organic matter as compared with the fine particles of titanium dioxide, problems arise such as low decomposition efficiency, poor durability, and poor adsorptivity of the organic matter.
As described in Japanese Unexamined Patent Application, First Publication No. Hei 6-315614A, a photocatalyst can be used which is produced by using a fluororesin as a binder, kneading photocatalytic particles with the fluororesin, extruding the kneaded mixture through an extruder, and rolling it to form a sheet. In this case, the fluororesin is not decomposed by the photocatalyst. However, according to the method of forming the sheet of the photocatalyst, the binding force between the photocatalyst powder and the fluororesin is increased by forming under the conditions of a temperature of 350 to 400° C. and a pressure of 200 to 300 kg/cm2, and therefore the photocatalyst powder is embedded into the fluororesin and the content of the photocatalyst powder at the surface of the resulting sheet decreases, thus reducing the active surface of the sheet. Also, the content of the fluororesin must be increased to 50% by weight or more in order to increase the strength of the sheet, thus resulting in a high manufacturing cost.
In addition to insufficient long-term water resistance, the granular photocatalytic material comprising photocatalytic particles and a filler had problems such that a chlorine-, sulfur-, or nitrogen-based intermediate product or final product formed by the decomposition of the organic matter due to the photocatalyst lowered the activity of the photocatalyst and delayed the decomposition reaction.
Also, the granular photocatalytic material comprising photocatalytic particles and colloidal silica had a problem such that the mechanical strength was insufficient and was about ½ to ⅓ of that of the above granular photocatalytic material comprising photocatalytic particles and a filler.